Chair back adjusting mechanism

ABSTRACT

The present invention is about a chair back adjusting mechanism, and relates to the technical field of chairs. The chair back adjusting mechanism includes a chair back, which is movably disposed above a supporting surface of a chair seat and is provided with a connecting base at a side close to a fixed bracket, and the chair back is movably connected to the connecting base; the connecting base is provided with a first sleeve pipe at a side close to the fixed bracket, the fixed bracket is provided with a second sleeve pipe at a side close to the connecting base. The chair back is connected to a chair body by a sliding and elastic telescopic assembly, which reduces the user&#39;s feeling of fatigue and effectively relieves fatigue at the waist of sedentary people; and the chair back adjusting mechanism has a simple structure, which reduces the manufacturing cost.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No. 202123007620.2 with a filing date of Dec. 2, 2021. The content of the aforementioned application, including any intervening amendments thereto, are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Technical Field

The present utility model belongs to the technical field of chairs, and in particular, relates to a chair back adjusting mechanism.

2. Description of Related Art

A chair back is used to provide support to the back and waist of a user when he/she is in a sitting posture state. The support provided by the chair back of an existing chair is typically disposed to be fixed and immovable. The user has to change his/her sitting posture to allow the back to get close to and fit the chair back, thereby achieving support for the back. This has some limitations, which limit the sitting posture of the user. An existing adjusting mechanism is complicated in structure and high in manufacturing cost. Therefore, we propose a chair back adjusting mechanism.

BRIEF SUMMARY OF THE INVENTION

In view of the defects of the prior art, an objective of the present utility model is to provide a chair back adjusting mechanism to solve the problems raised in the above background art.

The objective of the present utility model can be achieved by the following technical solution: a chair back adjusting mechanism includes a chair back, which is movably disposed above a supporting surface of a chair seat, and a distance between the chair back and a fixed bracket is adjustable; the chair back is provided with a connecting base at a side close to the fixed bracket, and the chair back is movably connected to the connecting base; the connecting base is provided with a first sleeve pipe at a side close to the fixed bracket, the fixed bracket is provided with a second sleeve pipe at a side close to the connecting base, and the first sleeve pipe and the second sleeve pipe are sleeve-jointed coaxially and slidably; at least two sets of sliding guide structures are arranged in a circular array between radial directions of the first sleeve pipe and the second sleeve pipe;

The sliding guide structures include guide blocks and guide slots, the guide blocks are accommodated within the guide slots and slide along the guide slots, the guide blocks are disposed on the second sleeve pipe, and the guide slots are disposed in the first sleeve pipe; or the guide blocks are disposed on the first sleeve pipe, the guide slots are disposed in the second sleeve pipe, the guide slots are formed integrally with the sleeve pipe, and the guide blocks are formed integrally with the sleeve pipe or are independently disposed to be detachably connected to the sleeve pipe;

The chair back adjusting mechanism further includes a locking-up assembly, which is configured to fix the second sleeve pipe and the first sleeve pipe; and

The chair back adjusting mechanism further includes an elastic member, which is between axial directions of the second sleeve pipe and the first sleeve pipe.

As an optional solution of the present utility model, the first sleeve pipe is accommodated within the second sleeve pipe, the guide blocks are detachably connected to a peripheral side of the first sleeve pipe, and an inner wall of the second sleeve pipe is provided with the guide slots; or the guide blocks are detachably connected to the inner wall of the second sleeve pipe, and an outer wall of the first sleeve pipe is provided with the guide slots.

As an optional solution of the present utility model, the first sleeve pipe is accommodated within the second sleeve pipe, the guide blocks are formed integrally with a peripheral side of the first sleeve pipe, and an inner wall of the second sleeve pipe is provided with the guide slots; or the guide blocks are formed integrally with the inner wall of the second sleeve pipe, and an outer wall of the first sleeve pipe is provided with the guide slots.

As an optional solution of the present utility model, the second sleeve pipe is accommodated within the first sleeve pipe, the guide blocks are detachably connected to a peripheral side of the second sleeve pipe, and an inner wall of the first sleeve pipe is provided with the guide slots; or the guide blocks are detachably connected to the inner wall of the first sleeve pipe, and an outer wall of the second sleeve pipe is provided with the guide slots.

As an optional solution of the present utility model, the second sleeve pipe is accommodated within the first sleeve pipe, the guide blocks are formed integrally with a peripheral side of the second sleeve pipe, and an inner wall of the first sleeve pipe is provided with the guide slots; or the guide blocks are formed integrally with the inner wall of the first sleeve pipe, and an outer wall of the second sleeve pipe is provided with the guide slots.

As an optional solution of the present utility model, the elastic member includes a spring, which has one end fixedly clamped with the connecting base and the other end fixedly clamped with a connecting plate; a distance between the connecting plate and a cover plate is adjustable so as to adjust a supporting force of the chair back; and the cover plate is fixedly connected to the fixed bracket.

As an optional solution of the present utility model, the cover plate is provided with an adjusting lever, which is rotatably connected to the cover plate; and the connecting plate is connected to the adjusting lever through threads.

As an optional solution of the present utility model, the locking-up assembly includes a locking-up bolt, which is slidably connected to the second sleeve pipe or the first sleeve pipe and extends or retracts along a radial direction; an outer periphery of the first sleeve pipe or the second sleeve pipe is axially provided with a plurality of positioning holes in an array; and the locking-up bolt is extendable to be inserted in any one of the positioning holes.

As an optional solution of the present utility model, a bottom end of the fixed bracket is provided with a lower support plate that is connected to the chair seat; a bottom surface of the lower support plate is provided with a clamping slot that is slidably connected to a sliding rail of the chair seat; and the lower support plate is provided with a connecting rod that penetrates through the entire clamping slot.

As an optional solution of the present utility model, a top end of the first sleeve pipe is provided with a straight slot, a rabbet of which is internally provided with a cushion pad; the cushion pad is accommodated in the rabbet at the top end of the first sleeve pipe and is fixedly connected to an end surface of the first sleeve pipe; an end surface of the second sleeve pipe at a side close to the first sleeve pipe is provided with a limiting retainer ring; the limiting retainer ring is located at a side of the cushion pad close to the connecting base; and the limiting retainer ring is detachably connected to the second sleeve pipe.

The present utility model has the following beneficial effects: by slidably connecting the chair back to the chair body and providing an elastic support by the elastic member, the chair back always keeps fitting the user's back and moves along with the user, which reduces the user's feeling of fatigue and relieves fatigue at the waist of sedentary people; and meanwhile, by adjusting the compression amount of the spring to adjust the support level of the chair back, the user requirements of different users can be met; and moreover, the present utility model has a simple structure, which reduces the manufacturing cost.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

To describe the technical solutions in the embodiments of the present utility model or in the prior art more clearly, the following briefly introduces the accompanying drawings to be used in the description of the embodiments or the prior art. Obviously, a person of ordinary skills in the art may still derive other drawings from these accompanying drawings without creative efforts.

FIG. 1 is a schematic diagram of an overall structure according to the present utility model;

FIG. 2 is a schematic structural diagram of a connecting base according to the present utility model;

FIG. 3 is a schematic structural diagram of a fixed bracket according to the present utility model;

FIG. 4 is a schematic structural diagram of a lifting adjusting mechanism according to the present utility model;

FIG. 5 is a sectional view according to the present utility model;

FIG. 6 is a schematic diagram of a first sleeve pipe in another state according to an embodiment of the present utility model; and

FIG. 7 is a schematic diagram of a second sleeve pipe in another state according to an embodiment of the present utility model.

In the drawings, reference signs are as follows: 1, chair back; 2, adjusting plate; 3, connecting base; 31, first sleeve pipe; 4, fixed bracket; 41, second sleeve pipe; 42, lower support plate; 43, limiting retainer ring; 32, cushion pad; 5, spring; 6, connecting plate; 7, adjusting lever; 8, cover plate; 9, locking-up bolt; 301, first positioning slot; 311, guide slot; 401, second positioning slot; 312, positioning hole; 101, groove; 102, helical tooth slot; 22, swing rod; 211, fan-shaped slot; 221, limiting rod; 411, guide block; 421, clamping slot; and 422, connecting rod.

DETAILED DESCRIPTION OF THE INVENTION

The technical solutions in the embodiments of the present utility model will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present utility model. Obviously, the embodiments described are merely some instead of all of the embodiments of the present utility model. Based on the embodiments of the present utility model, all other embodiments achieved by those ordinarily skilled in the art without making creative efforts shall fall within the protection scope of the present utility model.

Referring to FIGS. 1 to 7 , in an embodiment of the present utility model, a chair back adjusting mechanism includes a chair back 1, which is movably disposed above a supporting surface of a chair seat, and a distance between the chair back 1 and a fixed bracket 4 is adjustable; the chair back 1 is provided with a connecting base 3 at a side close to the fixed bracket 4, and the chair back 1 is movably connected to the connecting base 3; the connecting base 3 is provided with a first sleeve pipe 31 at a side close to the fixed bracket 4, the fixed bracket 4 is provided with a second sleeve pipe 41 at a side close to the connecting base 3, and the first sleeve pipe 31 and the second sleeve pipe 41 are sleeve-jointed coaxially and slidably; the first sleeve pipe 31 may be accommodated within the second sleeve pipe 41, or the second sleeve pipe 41 may be accommodated within the first sleeve pipe 31; and at least two sets of sliding guide structures are arranged in a circular array between radial directions of the first sleeve pipe 31 and the second sleeve pipe 41.

The sliding guide structures include guide blocks 411 and guide slots 311; the guide blocks 411 are accommodated within the guide slots 311 and slide along the guide slots 311; the guide blocks 411 are made of a metallic material, such as a copper alloy and carbon steel.

The sliding guide structures include guide blocks 411 and guide slots 311, the guide blocks 411 are accommodated within the guide slots 311 and slide along the guide slots 311, the guide blocks 411 are disposed on the second sleeve pipe 41, and the guide slots 311 are disposed in the first sleeve pipe 31; or the guide blocks 411 are disposed on the first sleeve pipe 31, the guide slots 311 are disposed in the second sleeve pipe 41, the guide slots 311 are formed integrally with the sleeve pipe, and the guide blocks 411 are formed integrally with the sleeve pipe or are independently disposed to be detachably connected to the sleeve pipe.

The sliding guide structures may be specifically configured as in the following several embodiments.

Embodiment 1: The first sleeve pipe 31 is accommodated within the second sleeve pipe 41, the guide blocks 411 are detachably connected (for example, via bolt fixation) to a peripheral side of the first sleeve pipe 31, and an inner wall of the second sleeve pipe 41 is provided with the guide slots 311; or the guide blocks 411 are detachably connected to the inner wall of the second sleeve pipe 41, and an outer wall of the first sleeve pipe 31 is provided with the guide slots 311, as shown in FIG. 6 and FIG. 7 .

Embodiment 2: The first sleeve pipe 31 is accommodated within the second sleeve pipe 41, the guide blocks 411 are formed integrally with a peripheral side of the first sleeve pipe 31, and an inner wall of the second sleeve pipe 41 is provided with the guide slots 311; or the guide blocks 411 are formed integrally with the inner wall of the second sleeve pipe 41, and an outer wall of the first sleeve pipe 31 is provided with the guide slots 311. The states are shown as in FIG. 2 and FIG. 3 .

Embodiment 3: The second sleeve pipe 41 is accommodated within the first sleeve pipe 31, the guide blocks 411 are detachably connected (for example, via bolt fixation) to a peripheral side of the second sleeve pipe 41, and an inner wall of the first sleeve pipe 31 is provided with the guide slots 311; or the guide blocks 411 are detachably connected to the inner wall of the first sleeve pipe 31, and an outer wall of the second sleeve pipe 41 is provided with the guide slots 311.

Embodiment 4: The second sleeve pipe 41 is accommodated within the first sleeve pipe 31, the guide blocks 411 are formed integrally with a peripheral side of the second sleeve pipe 41, and an inner wall of the first sleeve pipe 31 is provided with the guide slots 311; or the guide blocks 411 are formed integrally with the inner wall of the first sleeve pipe 31, and an outer wall of the second sleeve pipe 41 is provided with the guide slots 311.

The chair back adjusting mechanism further includes a locking-up assembly, which is configured to fix the second sleeve pipe 41 and the first sleeve pipe 31.

The chair back adjusting mechanism further includes an elastic member, which is between the axial directions of the second sleeve pipe 41 and the first sleeve pipe 31.

When in use, the chair back 1 supports the user's back, and the elastic member keeps the chair back 1 supporting the user's back. When the user's body moves, the chair back 1 follows the movement to always keep supporting the user's back, which reduces the user's feeling of fatigue and relieves the waist fatigue of sedentary people. Meanwhile, the first sleeve 31 and the second sleeve pipe 41 are guided during sliding by a self-mechanism, without the arrangement of an additional sliding assembly. Moreover, the structure is simple and is convenient to process, which reduces the total manufacturing cost.

Preferably, as shown in FIG. 5 , a spring 5 is used as the elastic member, with one end fixedly clamped with the first sleeve pipe 31 and the other end fixedly clamped with the connecting plate 6; a distance between the connecting plate 6 and the cover plate 8 is adjustable so as to adjust the supporting force of the chair back 1; and the cover plate 8 is fixedly connected to the fixed bracket 4. The support level of the chair back 1 can be adjusted by adjusting the distance between the connecting plate 6 and the cover plate 8 and adjusting the compression amount of the spring 5, thereby meeting different needs. In some scenarios, a pneumatic mechanism, such as a vacuum cylinder, an air sac and a connecting block made of a material with good resilience, may also be used.

Preferably, a top end of the first sleeve pipe 31 is provided with a straight slot, a rabbet of which is internally provided with a cushion pad 32; the cushion pad 32 is accommodated in the rabbet at the top end of the first sleeve pipe 31 and is fixedly connected to an end surface of the first sleeve pipe 31; and an end surface of the second sleeve pipe 41 at a side close to the first sleeve pipe 31 is provided with a limiting retainer ring 43. As shown in FIG. 6 , the limiting retainer ring 43 is located at a side of the cushion pad 32 close to the connecting base 3, and the limiting retainer ring 43 is fixedly connected to the second sleeve pipe 41 by a screw, thereby limiting the first sleeve pipe 31 and the second sleeve pipe 41 and preventing them from separation. Meanwhile, the cushion pad 32 has a cushion effect, which on one hand alleviates the deformation caused by collisions between the first sleeve pipe 31 and the second sleeve pipe 41, and on the other hand can reduce noises.

In some other embodiments, the compression amount of the spring 5 is adjusted in the following fashion. As shown in FIG. 1 , the adjusting lever 7 is disposed on the cover plate 8 and is rotatably connected to the cover plate 8; and the connecting plate 6 is connected to the adjusting lever 7 through threads. That is, the compression amount of the spring 5 is adjusted by rotating the adjusting lever 7 to adjust the distance between the connecting plate 6 and the cover plate 8, thereby adjusting the support level. In another embodiment, the distance between the connecting plate 6 and the cover plate 8 may also be adjusted by a cam mechanism.

Specifically, as shown in FIG. 1 , the locking-up assembly includes a limiting bolt 9, which is slidably connected to the second sleeve pipe 41 and extends or retracts along a radial direction of the second sleeve pipe 41; the outer periphery of the first sleeve pipe 31 is axially provided with a plurality of positioning holes 312 in an array; and the limiting bolt 9 is extendable to be inserted in any one of the positioning holes 312. Therefore, the operation is convenient.

In some application scenarios, a bottom end of the fixed bracket 4 is provided with a lower support plate 42 that is connected to the chair seat. A bottom surface of the lower support plate 42 is provided with a clamping slot 421 that is slidably connected to a sliding rail of the chair seat. The lower support plate 42 is provided with a connecting rod 422 that penetrates through the entire clamping slot 421. The connecting rod 422 is configured to fixedly connect the lower support 42 with the chair seat. A connecting plate disposed at a lower end of the chair seat is configured to connect the lower support plate 42 of the fixed bracket 4. The lower support plate 42 is fixedly connected to the connecting plate by the clamping slot 421 and the connecting rod 422. The connecting plate is provided with a waist-shaped hole, in which the connecting rod 422 is disposed. When the connecting rod 422 is located at a side of the waist-shaped hole away from the chair seat, the fixed bracket 4 may be counterclockwise flipped down.

In some application scenarios, the chair seat 1 is slidably connected to the connecting base 3; an adjusting plate 2 is disposed between the chair back 1 and the connecting base 3, and is fixedly connected to the connecting base 3; the chair back 1 moves up and down along the adjusting plate 2; the adjusting plate 2 is provided with a height adjusting assembly, which is configured to adjust the height of the chair back 1 so as to cater for people of different heights. The position of the chair back 1 can be adjusted based on the height of a user to meet the requirement for supporting the waist.

Preferably, as shown in FIG. 1 and FIG. 4 , the height adjusting assembly includes a swing rod 22 and a limiting rod 221. A side face of the adjusting plate 2 at a side away from the chair back 1 is provided with a fan-shaped slot 211, in which the swing rod 22 is accommodated. One end of the swing rod 22 is articulated with the adjusting plate 2, with an articulated section provided with a torsion spring for keeping the swing rod 22 in a vertical state. A side face of the chair back 1 at a side close to the adjusting plate 2 is provided with a groove 101, in which a plurality of helical tooth slots 102 are arranged in an array along a vertical direction, and the helical tooth slots 102 have a downward tooth slot direction. The limiting rod 221 is fixed at an end of the swing rod 22 away from the articulated section, and extends through the adjusting plate 2 to be inserted in one of the helical tooth slots 102. When the position of the chair back 1 needs to be adjusted up, the chair back 1 is pulled upwards, the limiting rod 221 slides to a next tooth slot along a tooth surface of a current helical tooth slot 102 so as to support the chair back 1, and the torsion spring disposed on the swing rod 22 keeps the limiting rod 221 inserted in the tooth slot of helical tooth slot 102. When the chair back 1 moves to allow the limiting rod 221 to move to a bottommost helical tooth slot 102, the limiting rod 221 gets rid of the limitation from the helical tooth slot 102. That is, the chair back 1 may move downwards.

In the description of the present utility model, it should be understood that the terms such as “up”, “down”, “left”, and “right” indicate orientations or positional relations based on the orientations or position relations as shown in the accompanying drawings only for the purposes of describing the present utility model and simplifying the description, instead of indicating or implying that a mentioned device or element must have a specific orientation or must be constructed and operated in a specific orientation. Therefore, these terms should not be construed as limiting the present utility model.

In addition, the terms “first” and “second” are only for descriptive purposes, and shall not to be construed as indicating or implying relative importance or implicitly indicating the number of a mentioned technical feature. In the description of the present utility model, “a plurality of” means two or more, unless otherwise clearly defined.

For those skilled in the art, it can be understood that a variety of changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present utility model. Therefore, from any point, the embodiments should be considered as instructive and nonrestrictive. The scope of the present utility model is defined by the appended claims rather than the above description. The preferred embodiments of the present utility model are not intended to limit the present utility model. Any amendments, equivalent substitutions, improvements and the like made within the spirit and principle of the present utility model should be included within the scope of protection of the present utility model. 

What is claimed is:
 1. A chair back adjusting mechanism comprising a chair back (1), characterized in that the chair back (1) is movably disposed above a supporting surface of a chair seat, and a distance between the chair back (1) and a fixed bracket (4) is adjustable; the chair back (1) is provided with a connecting base (3) at a side close to the fixed bracket (4), and the chair back (1) is movably connected to the connecting base (3); the connecting base (3) is provided with a first sleeve pipe (31) at a side close to the fixed bracket (4), the fixed bracket (4) is provided with a second sleeve pipe (41) at a side close to the connecting base (3), and the first sleeve pipe (31) and the second sleeve pipe (41) are sleeve jointed coaxially and slidably; at least two sets of sliding guide structures are arranged in a circular array between radial directions of the first sleeve pipe (31) and the second sleeve pipe (41); the sliding guide structures comprise guide blocks (411) and guide slots (311), the guide blocks (411) are accommodated within the guide slots (311) and slide along the guide slots (311), the guide blocks (411) are disposed on the second sleeve pipe (41), and the guide slots (311) are disposed in the first sleeve pipe (31); or the guide blocks (411) are disposed on the first sleeve pipe (31), the guide slots (311) are disposed in the second sleeve pipe (41), the guide slots (311) are formed integrally with the sleeve pipe, and the guide blocks (411) are formed integrally with the sleeve pipe or are independently disposed to be detachably connected to the sleeve pipe; the chair back adjusting mechanism further comprises a locking-up assembly, which is configured to fix the second sleeve pipe (41) and the first sleeve pipe (31); and the chair back adjusting mechanism further comprises an elastic member, which is between axial directions of the second sleeve pipe (41) and the first sleeve pipe (31).
 2. The chair back adjusting mechanism according to claim 1, characterized in that the first sleeve pipe (31) is accommodated within the second sleeve pipe (41), the guide blocks (411) are detachably connected to a peripheral side of the first sleeve pipe (31), and an inner wall of the second sleeve pipe (41) is provided with the guide slots (311); or the guide blocks (411) are detachably connected to the inner wall of the second sleeve pipe (41), and an outer wall of the first sleeve pipe (31) is provided with the guide slots (311).
 3. The chair back adjusting mechanism according to claim 1, characterized in that the first sleeve pipe (31) is accommodated within the second sleeve pipe (41), the guide blocks (411) are formed integrally with a peripheral side of the first sleeve pipe (31), and an inner wall of the second sleeve pipe (41) is provided with the guide slots (311); or the guide blocks (411) are formed integrally with the inner wall of the second sleeve pipe (41), and an outer wall of the first sleeve pipe (31) is provided with the guide slots (311).
 4. The chair back adjusting mechanism according to claim 1, characterized in that the second sleeve pipe (41) is accommodated within the first sleeve pipe (31), the guide blocks (411) are detachably connected to a peripheral side of the second sleeve pipe (41), and an inner wall of the first sleeve pipe (31) is provided with the guide slots (311); or the guide blocks (411) are detachably connected to the inner wall of the first sleeve pipe (31), and an outer wall of the second sleeve pipe (41) is provided with the guide slots (311).
 5. The chair back adjusting mechanism according to claim 1, characterized in that the second sleeve pipe (41) is accommodated within the first sleeve pipe (31), the guide blocks (411) are formed integrally with a peripheral side of the second sleeve pipe (41), and an inner wall of the first sleeve pipe (31) is provided with the guide slots (311); or the guide blocks (411) are formed integrally with the inner wall of the first sleeve pipe (31), and an outer wall of the second sleeve pipe (41) is provided with the guide slots (311).
 6. The chair back adjusting mechanism according to claim 1, characterized in that the elastic member comprises a spring (5), which has one end fixedly clamped with the connecting base (3) and the other end fixedly clamped with a connecting plate (6); a distance between the connecting plate (6) and a cover plate (8) is adjustable so as to adjust a supporting force of the chair back (1); and the cover plate (8) is fixedly connected to the fixed bracket (4).
 7. The chair back adjusting mechanism according to claim 6, characterized in that the cover plate (8) is provided with an adjusting lever (7), which is rotatably connected to the cover plate (8); and the connecting plate (6) is connected to the adjusting lever (7) through threads.
 8. The chair back adjusting mechanism according to claim 1, characterized in that the locking-up assembly comprises a locking-up bolt (9), which is slidably connected to the second sleeve pipe (41) or the first sleeve pipe (31) and extends or retracts along a radial direction; an outer periphery of the first sleeve pipe (31) or the second sleeve pipe (41) is axially provided with a plurality of positioning holes (312) in an array; and the locking-up bolt (9) is extendable to be inserted in any one of the positioning holes (312).
 9. The chair back adjusting mechanism according to claim 1, characterized in that a bottom end of the fixed bracket (4) is provided with a lower support plate (42) that is connected to the chair seat; a bottom surface of the lower support plate (42) is provided with a clamping slot (421) that is slidably connected to a sliding rail of the chair seat; and the lower support plate (42) is provided with a connecting rod (422) that penetrates through the entire clamping slot (421).
 10. The chair back adjusting mechanism according to claim 1, characterized in that a top end of the first sleeve pipe (31) is provided with a straight slot, a rabbet of which is internally provided with a cushion pad (32); the cushion pad (32) is accommodated in the rabbet at the top end of the first sleeve pipe (31) and is fixedly connected to an end surface of the first sleeve pipe (31); an end surface of the second sleeve pipe (41) at a side close to the first sleeve pipe (31) is provided with a limiting retainer ring (43); the limiting retainer ring (43) is located at a side of the cushion pad (32) close to the connecting base (3); and the limiting retainer ring (43) is detachably connected to the second sleeve pipe (41). 